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AugustKarlstedt opened this issue Oct 3, 2024 · 4 comments
Closed

IndexErrors are handled differently than other exceptions #573

AugustKarlstedt opened this issue Oct 3, 2024 · 4 comments
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@AugustKarlstedt
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AugustKarlstedt commented Oct 3, 2024 •
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When a parse action raises an IndexError, it does not bubble up the exception message as it would other types of exceptions. This makes it hard to debug how/why my parse action is failing if it raises an IndexError.

minimal example:

import pyparsing as pp

def parse_hello(
    _string: str, _location: int, _tokens: pp.ParseResults
) -> None:
    print(f"parsed {_tokens}")
    raise Exception('this works ok')

def parse_world(
    _string: str, _location: int, _tokens: pp.ParseResults
) -> None:
    print(f"parsed {_tokens}")
    raise IndexError('this does not')

hello = pp.Keyword("hello").set_parse_action(parse_hello)
world = pp.Keyword("world").set_parse_action(parse_world)
parser = pp.ZeroOrMore(hello | world)

parser.run_tests([
    "hello",
    "world"
])

outputs

parsed ['hello']

hello
FAIL-EXCEPTION: Exception: this works ok
parsed ['world']

world
world
^
ParseException: Expected end of text, found 'world'  (at char 0), (line:1, col:1)
FAIL: Expected end of text, found 'world'  (at char 0), (line:1, col:1)

which properly bubbles up the exception raised when parsing "hello" but fails with an ambiguous error when parsing "world".

It should print FAIL-EXCEPTION: IndexError: this does not even if the parse action raises an IndexError
@ptmcg ptmcg self-assigned this Oct 3, 2024
ptmcg added a commit that referenced this issue Oct 3, 2024
@ptmcg
Handle IndexErrors raised in a parse action so they do not get masked…
0fcc013 
… by pyparsing exception handlers (Issue #573)
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ptmcg commented Oct 3, 2024

Thanks - I actually had some code around this as being expected behavior, but giving it a re-think, I worked out how to keep parse action IndexErrors from getting misread as ParserElement.parseImpl IndexErrors. In the bargain, I also enhanced the run_tests output to now indicate if an exception is raised, if it is raised in a parse action, and reports the parse action by name. For your case, I now get this output:

parsed ['hello']


hello
FAIL-EXCEPTION (raised in parse action 'parse_hello'): Exception: this works ok
parsed ['world']


world
FAIL-EXCEPTION (raised in parse action 'parse_world'): IndexError: this does not

This fix will go out in the next release.

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ptmcg commented Oct 5, 2024

Please try again using 3.2.0rc1, which I just pushed to PyPI.

@AugustKarlstedt
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Just tested in a non-trivial codebase and the error message now shows exactly where the underlying IndexError happens. Much appreciated for the improvements here!

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ptmcg commented Oct 13, 2024

Released in 3.2.0, closing.

@ptmcg ptmcg closed this as completed Oct 13, 2024
@FliegendeWurst FliegendeWurst mentioned this issue Feb 2, 2025
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